Partial sums of A001891.

Terms

a(0) =1a(1) =5a(2) =15a(3) =36a(4) =76a(5) =148a(6) =273a(7) =485a(8) =839a(9) =1424a(10) =2384a(11) =3952a(12) =6505a(13) =10653a(14) =17383a(15) =28292a(16) =45964a(17) =74580a(18) =120905a(19) =195885a(20) =317231a(21) =513600a(22) =831360a(23) =1345536a(24) =2177521a(25) =3523733a(26) =5701983a(27) =9226500a(28) =14929324a(29) =24156724